Look for a heavy gauge deck. If you're in for a penny, go in for a pound and buy from an outdoor power dealer and don't get the consumer grade units you find at Home Depot. Yes, the up-front cost is about 30% to 50% more, but you get a lot more machine for the dollar.
For our farm, I finally settled on a Ferris 52" with a 28 horse Briggs twin. We've only had it a season, but it is impressive. Fast, smooth, TOUGH so far. And all the blade spindles and individual parts are replaceable if necessary. What sold me on the Ferris was the gauge of the deck metal plus the spring suspension. Really makes a difference. The farmhand who usually does the upkeep is, well... lets' just say crusty. Opposed to change. Set in his ways. A pain in my...rear... at times. He's also got a bad back (as do I), and I really felt for him bouncing around on the JD. He scowled at me for weeks when I told him I was buying a ZT mower to replace the JD tractor we'd had out there for 12 years. He growled even more when I loaded up the JD and brought it to my house- I think he wanted to just keep using it. But after about 5 hours on the hour meter, he was LOVING the Ferris. I think he'd shoot me if I gave him the JD back! So I bounce around on it on the town lot and hurt *my* back... :-/